1. Field of the Invention
The present invention relates to flow meters employed for the measurement of fluid flow through a fluid pipe line or conduit.
2. Description of the Prior Art
Many approaches to measuring the flow of fluid through a pipe line are employed in the prior art. Typical flow meters employ either a spinning element or a ball in a track. In the meters employing a spinning element the element usually includes several paddles that interact with fluid flowing through the meter causing rotation of the element. This rotation is then measured. Such a prior art arrangement is difficult to assemble and is subject to continual maintenance requirements due to the complexity of the element's structure and its low friction mounting in the housing.
The meters that employ a ball bounded within a track direct all or a portion of the fluid flow through a tangential inlet in the valve allowing the fluid to impinge upon the ball causing the ball to rotate within the track. This rotation is then measured in order to determine the flow rate through the meter. One of the difficulties in using this prior art meter is that due to the centrifugal force of fluid passing through the meter, the fluid can experience a pressure drop and a sharp increase in fluid velocity depending on the arrangement of the inlet and outlet in the meter. These changes in the fluid can substantially reduce the accuracy of the meter.
One prior art procedure for preventing a pressure drop and a sharp increase in fluid velocity is to employ a tangential outlet in the meter. In this manner, once fluid enters the meter, it is directed to a circular track whereupon the fluid flows around the track until it encounters the outlet. Since the fluid does not change its direction of flow in entering the tangential outlet, smoother flow of the fluid out of the valve results avoiding a large pressure drop and a sharp increase in fluid velocity. In addition, the tangential positioning of the outlet allows the centrifugal force of the fluid that is developed as it flows around the track to assist rather than hamper the exit of fluid through the outlet, thus further limiting the pressure drop and the increase in fluid velocity.
The employment of a tangential outlet in combination with a tangential inlet, however, results in a meter that is less compact and necessitates a change in the direction of the fluid line in order to be installed. Moreover, this construction prevents the measurement of fluid flow in a bidirectional manner thus limiting its use to one way flow.
To overcome some of these problems related to tangentially positioned outlets, some prior art meters incorporate a set of vanes adjacent an axial outlet to direct fluid from the interior of the meter to the outlet. Such a meter is disclosed in U.S. Pat. No. 3,805,609. These meters, however, employ a tangential object and are incapable of measuring bidirectionally and of being mounted in-line with the fluid line.